Efficacy of soyfoods and soybean isoflavone supplements for alleviating menopausal symptoms is positively related to initial hot flush frequency

Soy has received attention as an alternative to conventional hormone replacement therapy (HRT) largely because it is a unique dietary source of isoflavones. Isoflavones are diphenolic compounds that have both hormonal and nonhormonal properties and are considered to be selective estrogen receptor modulators. The estrogen-like effects of isoflavones in combination with the low reported frequency of hot flushes in Japan has prompted investigation of the effect of soy on menopausal symptoms. The purpose of this review is to evaluate the efficacy of soyfoods and isoflavone supplements for the alleviation of hot flushes. Nineteen trials (13 using a parallel design) involving more than 1,700 women were identified. Six trials were excluded from analysis: two that involved breast cancer patients, two that reported data on severity but not hot flush frequency, one that was not blinded, and one that did not include a control group. Based on a simple regression analysis of the remaining data set (13 trials), there was a statistically significant relationship (P =.01) between initial hot flush frequency and treatment efficacy. Initial hot flush frequency explained about 46% of the treatment effects, and hot flush frequency decreased by about 5% (above placebo or control effects) for every additional initial hot flush per day in women whose initial hot flush frequency was five or more per day. Although conclusions based on this analysis should be considered tentative, the available data justify the recommendation that patients with frequent hot flushes consider trying soyfoods or isoflavone supplements for the alleviation of their symptoms.